Diffusion transfer printing of electron micrographs and envelope therefor



June 13, 1967 E, s. EMERSON 3,325,642

DIFFUSION TRANSFER PRINTING OF ELECTRON MICROGRAPHS AND ENVELOPE THEREFOR Filed Dec. 17, 1962 INVENTOR ATTORNEYS United States Patent C) Filed Dec. 17, 1962, Ser. No. assess 5 Claims. or. 250-495 This invention relates to the processing of photosensitive elements exposed in an electron microscope and to a novel product and process for use therein.

In the past, in electron microscopy, a lantern slide, i.e., a glass plate or glass-backed photographic emulsion, has been used to record an image of the specimen under study. Such a method contains a number of inherent disadvantages which result in inefficient use of the electron microscope, due primarily to time loss. One serious disadvantage is the necessity of removing an exposed lantern slide from the electron microscope, transporting the lantern slide to a darkroom, and there developing the lantern slide by means of a wet process, the electron microscope is operated in a darkened area and, due to the environmental conditions necessary for the operation of the electron microscope, it is necessary to locate the darkroom facilities in a separate room. Therefore, in order to process a nexposed lantern slide, it is necessary to pass through a lighted area into a darkroom. As a result, there is a time loss in the transporting, processing and examination of the photographic image before the study of the specimen can be continued as well as time loss involved in once again adapting the vision of the operator to the darkened room. It has now been found that a photosensitive element comprising an emulsion on a flexible support can be exposed in the electron microscope, removed and processed by means of the diffusion transfer process, in the same room with the electron microscope to give both a useful positive and negative of superior quality.

Objects of the invention are to provide, as a photographic product, a developing envelope comprising an image-receiving element and a cover sheet, said image-receiving element and said cover sheet defining an area therebetween adapted to receive an exposed photosensitive element, an entrance port or slit for the insertion therebetween of the exposed photosensitive element, means for releasably confining a processing solution, and means for entrapping the excess processing solution after said processing solution has been spread between said exposed photcsensitive element and said image-receiving element.

Still another object of the invention is to provide a process wherein a photosensitive element comprising an emulsion on a flexible support is exposed in an electron microscope and the thus-exposed photosensitive element is developed by diffusion transfer processing to provide a positive and a negative image.

Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claim.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection wtih the accompanying drawing wherein:

FIGURE 1 is an exploded perspective view of the developing envelope of this invention; and

FIG. 2 is a perspective sectional view of the developing envelope showing the exposed negative inserted therein and the relationship of the components prior to the release of the processing solution.

The present invention involves a product which comprises an opaque support, preferably carrying an imagereceiving layer, a rupturable container holding liquid photographic processing reagents, on said support, a lightproof cover sheet positioned over and spaced apart from said support to provide an envelope-like chamber for receiving an exposed photosensitive element. Development of the exposed photosensitive element is carried out according to the diffusion transfer process whereby the controlled and progressive application of mechanical stress to the structure results in rupture of said container, thereby effecting release and spreading of the liquid reagent between the exposed photosensitive element and the image-receiving layer. The transfer process, in one form thereof, may be said to be performed through permeation of the photographically exposed photosensitive surface by the liquid reagent, development of a latent image formed in the exposed emulsion by a photographic developing agent; dissolving undeveloped silver halide present in unexposed areas of the emulsion and by transporting it, in the form of a soluble silver complex, from the emulsion to the print-carrying layer so as to form a positive image in the latter. Examples of photographic materials suitable for use in a photographic process of the type contemplated herein or of related processes now are well known, and are, for example, set forth in detail in Patents Nos. 2,543,181, 2,559,643, 2,614,926, 2,647,049 and 2,647,056, all issued to Edwin H. Land. An example of a commercially available film for obtaining both a negative and a positive is that sold by Polaroid Corporation, Cambridge, Mass, under the designation Type 55 P/N.

Prior to the present invention, photographic images of specimens under examination in an electron microscope were obtained by exposing the glass lantern slide in the electron microscope, removing it from the microscope, transporting it to a darkroom where it would be developed by means of a wet process and examining the resultant image to determine whether the desired image with the proper quality had been obtained. Since the darkroom must be physically separate from the room containing the electron microscope, a considerable amount of lost time results from physically transporting the exposed lantern slide, developing it and waiting to determine the quality of the image before study on the microscope can be continued. It is also necessary to remove the specimen from the electron beam while awaiting processing and evaluation of the lantern slide to prevent destruction of the specimen. The necessity of repeated darkness adaptation of the operator of the electron microscope as a result of passing from lighted areas into the dark area wherein the electron microscope is operated is also responsible for time loss. The electron microscope is operated under a vacuum; therefore, it is necessary that the lantern slides be degassed and stored under a vacuum prior to use. Such a step has been found to be time consuming. Since lantern slides comprise a glass-backed photographic emulsion, any quantity of bulky and fragile lantern slides present storage as well as processing difficulties. Processing by a Wet process may result in damage or destruction by careless handling. The image quality of lantern slides frequently leaves something to be desired in that the images comprise black or white areas without a grey scale. The preparation of enlargements from lantern slides which must be carried out in a step separate from the processing of the plate itself is limited to ten times enlargement, due to the graininess of the image, which is objectionable at magniiications above ten times.

Utilizing the novel photographic product of this invention, an unwieldy and fragile glass plate emulsion can be replaced by a photosensitive element comprising an emulsion on a flexible support which can be exposed in the electron microscope and processed by diffusion transfer process in the novel developing envelope of this invention. Since the processing of the exposed photosensitive element in the developing envelope of this invention is a substantially dry process carried out in a self-contained unit, such processing may be accomplished in the room with the electron microscope and examined under a safe light. A positive image is available for evaluation in a matter of seconds and additional exposures may be made or the study of the specimen continued with a minimum of lost time due to processing delays, delays due to the necessity of light accommodation of the operator or delays due to removing and reinserting the specimen in the electron beam. In accordance with this invention, processing the exposed photosensitive element in the developing envelope of this invention provides a positive image available immediately for study, as well as a negative that may be later utilized to provide enlarged reproductions of the image. Procedures for obtaining a recoverable, fully developed and fixed negative concurrently with the formation of a positive silver image are disclosed in the copending application of Edwin H. Land, Meroe M. Morse and Elizabeth L. Yankowski, Serial No. 94,451, filed March 9, 1961.

Reference is now made to the drawings wherein there is illustrated a typical developing envelope of this invention. FIGURE 1 is an exploded perspective view of the developing envelope showing the relationship of each of the components to the other. The image-receiving element comprises an opaque support 30, an image-receiving layer 16, and a frangible container 11 of processing fluid on the leading end of said image-receiving element 10. On the trailing end of the receiving element 10 are positioned means 12 which provide a gap when the developing envelope is run between pressure rollers whereby the excess processing fluid from container 11 may be retained within the envelope in said gap and not squeezed out. Image-receiving layer 16 is substantially coextensive with the area of the photosensitive element to be processed and is adapted to receive a visible transfer image. A lighttight covering 13 is adhesively attached to said imagereceiving element 10 at edges 20 and 21 and preferably is intermittently attached to said image-receiving element 10 at spaced points 22 whereby said excess processing solution will be collected in channels and retained in the envelope. One end of said light-tight covering 13 comprises a hinged flap 17, fold 18 and tongue 19. Flap 17 is folded back so that fold 18 and the image-receiving element 10 define an opening whereby the exposed photosensitive element 15 may be inserted in the developing envelope and positioned so that the processing fluid from said container 11 will be spread between the silver halide emulsion stratum of said exposed photosensitive element 15 and said image-receiving layer 16. The desired positioning of the exposed photosensitive element is effected by limiting the length of the envelope-like chamber, e.g., by suitable means limiting further passage of the photosensitive element, such as the adhesive at points 22. After the exposed photosensitive element 15 has been inserted into the developing envelope, flap 17 may be folded over said entrance port and said tongue 19 caught over the trailing edge 24 of the receiving sheet to provide a closure for said developing envelope and a leader 25 for positioning said envelope and drawing it through a pair of pressure rollers. FIG. 2 shows a perspective cross-sectional view of the developing envelope with an exposed photosensitive element in position and ready for processing.

The novel photographic product of this invention may be used for processing exposed photosensitive elements from electron microscopes by the diffusion transfer process in the following manner. A. photosensitive element A comprising a photosensitive emulsion on a flexible suppor is exposed in an electron microscope, removed from said electron microscope, and inserted through the entrance port into the developing envelope with the photosensitive emulsion facing the image-receiving element and with the rupturable seal edge of the container 11 positioned between the two elements. The flap 17 of the envelope is closed over the entrance port and the envelope is pulled between a pair of rollers whereby the releasably confined fiuid from container 11 is spread between the superposed photosensitive element 15 and the image-receiving element 10 whereby a positive image will be formed on imagereceiving layer 16 and a fixed, recoverable negative will be formed on said exposed photosensitive element 15 according to the diffusion transfer processes above described. To facilitate separation of the positive image from the negative, the image-carrying area of said image-receiving element 10 may be appropriately perforated.

By processing photosensitive elements in the novel product of this invention, greater advantages in the use of the electron microscope and reproduction of images therefrom may be achieved than has heretofore been possible. For example, a superior image is formed which is grainless and with a good degree of contrast and a wide range grey scale which is not available with lantern slides. Enlargements up to 20 to 25 times may be made with ease from the recoverable negative processed in the developing envelope of this invention. If an enlargement of one million times is desired, the exposure with a lantern slide must be made with the electron microscope operating at a magnification of 100,000 whereas it is only necessary to operate the electron microscope at a magnification of 40,000 when a flexible backed photosensitive element is used. As stated above, the enlargements of this order of magnitude utilizing the above-described photosensitive elements show no appreciable grain while grain is apparent to an almost objectionable degree in the enlargements from lantern slides. By processing exposures from the electron microscope with the developing envelope of this invention, a gain of three in the output of the electron microscope may be achieved. It has also been found that the photosensitive elements may be degassed at a faster rate than the prior art lantern slides and may be maintained under a vacuum without any difficulty. The size and weight of flexible based negatives permit ready storage and easy handling and permit a greater number of exposures to be made without reloading the electron microscope, thus permitting more continuous operation. The flexible support for the silver halide emulsion is a plastic, such as cellulose acetate, polyester, or any of the other well-known plastic film bases.

It should be understood that while the exposed photosensitive elements are preferably processed in the novel developing envelope of this invention, they may also be processed by other structures utilizing the diffusion transfer process. It also will be understood that although the novel developing envelope finds particular utility in electron microscope photography, it also may be advantageously used where the photosensitive element is exposed in any other desired manner. Similarly, one may use this developing envelope with film units which do not give a recoverable negative.

In the preferred embodiment, the exposed photosensitive negative is processed in a light-tight developing envelope under a safe light in the electron microscope room. Alternatively, since the image is formed by the direct exposure of an electron beam and not by visible light it may be desirable to use a photosensitive element which does not contain sensitizers. In the alternative embodiment, it is not necessary that the cover sheet or image-receiving element be light opaque.

The developing envelope of this invention may also be used in processing photosensitive elements which have been exposed to other forms of corpuscular matter such, for example, as may be found in a proton microscope.

Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A photographic product comprising an opaque, flexible image-receiving element adapted for forming a photographic image thereon by diffusion transfer; an opaque flexible cover sheet secured in face-to-face relationship with said element to define a flexible envelope open at one end for insertion of an exposed photosensitive element; container means for releasably confining a photographic processing liquid positioned within said envelope so as to be capable of releasing said fluid between said imagereceiving element and an exposed photosensitive element inserted through said open end in superposition therewith; and closure means for closing said open end to provide an effectively light-tight envelope, said closure means comprising a hinged flap and tongue on said cover sheet, said flap being adapted to be folded over said open end and held in position by placing said tongue over said imagereceiving element.

2. A product as defined in claim 1 including means for positioning a photosensitive element inserted through said open end in superposition with said image-receiving element.

3. A product as defined in claim 1 including gap-providing means for providing a space between said image-receiving element and an exposed photosensitive element inserted through said open end during processing thereof, whereby to effect retention within said envelope of excess processing fluid released from said Container means during said processing.

4. A process of electron photomicroscopy comprising the steps of exposing a flexible photosensitive element to a beam of electrons while said element is held under a vacuum in an electron microscope; removing said photosensitive element from said microscope in the absence of actinic radiation and placing said exposed element in a flexible processing envelope in superposition with an image-receiving element; and spreading an aqueous alkaline processing composition between said superposed elements in said envelope to develop said exposed photosensitive element and to form a transfer image on said image-receiving element.

5. A process as defined in claim 4 wherein said envelope comprises a product as define-d in claim 1.

References Cited UNITED STATES PATENTS 2,360,871 10/1944 Griswold 25068 2,687,478 8/1954 Land. 2,781,181 2/1957 Adams 22962 OTHER REFERENCES Neblette: Photography, Its Materials and Processes,

page 379, pub. 1962, 6th edition.

NORMAN G. TORCHIN, Primary Examiner.

DONALD LEVY, Examiner. 

1. A PHOTOGRAPHIC PRODUCT COMPRISING AN OPAQUE, FLEXIBLE IMAGE-RECEIVING ELEMENT ADAPTED FOR FORMING A PHOTOGRAPHIC IMAGE THEREON BY DIFFUSION TRANSFER; AN OPAQUE FLEXIBLE COVER SHEET SECURED IN FACE-TO-FACE RELATIONSHIP WITH SAID ELEMENT TO DEFINE A FLEXIBLE ENEVLOPE OPEN AT ONE END FOR INSERTION OF AN EXPOSED PHOTOSENSITIVE ELEMENT; CONTAINER MEANS FOR RELEASABLY CONFINING A PHOTOGRAPHIC PROCESSING LIQUID POSITIONED WITHIN SAID ENVELOPE SO AS TO BE CAPABLE OF RELEASING SAID FLUID BETWEEN SAID IMAGERECEIVING ELEMENT AND AN EXPOSED PHOTOSENSITIVE ELEMENT INSERTED THROUGH SAID OPEN END IN SUPERPOSITION THEREWITH; AND CLOSURE MEANS FOR CLOSING SAID OPEN END TO PROVIDE AN EFFECTIVELY LIGHT-TIGHT ENVELOPE, SAID CLOSURE MEANS COMPRISING A HINGED FLAP AND TONGUE ON SAID COVER SHEET, SAID FLAP BEING ADATPED TO BE FOLDED OVER SAID OPEN END AND HELD IN POSITION BY PLACING SAID TONGUE OVER SAID IMAGERECEIVING ELEMENT. 